+2019 September 3; version 1.6.0
+ Fix bug in the rmr_rts_msg() function. If a return to sender message
+ failed, the source IP address was not correctly adjusted and could
+ cause the message to be "reflected" back to the sender on a retry.
+
+ Added the ability to set the source "ID" via an environment var
+ (RMR_SRC_ID). When present in the environment, the string will
+ be placed in to the message header as the source and thus be used
+ by an application calling rmr_rts_smg() to return a response to
+ the sender. If this environment variable is not present, the host
+ name (original behaviour) is used.
+